Gyroscope interface conversion circuit

Abstract: An interface circuit is provided to allow substitution of digital output rotation sensors such as fiber optic gyroscopes (13) or ring laser gyroscopes (77) in place of spinning mass gyroscopes. The pulses generated from the fiber optic gyroscope, or from a ring laser gyroscope are converted to a voltage representative of volts per degrees per second and are summed with an inverted (33) volts per degrees per second command (31) at an integrating summing amplifier (29, 27, 35) to result in an error signal in volts per degrees per second when there is a difference between the actual output of the gyroscope (13') and the command signal (31).

Description: This invention relates to an interface circuit which permits substitution of digital output rotation sensors in place of spinning mass analog rotation output sensors in existing analog output sensor configured systems. More specifically, the invention relates to an interface circuit which permits substitution of fiber optic gyroscopes or ring laser gyroscopes in place of spinning mass gyroscopes. A number of aircraft, satellites or other vehicles presently in use rely on spinning mass gyroscopes having an analog output for use in guidance of the vehicle. Typically, such gyroscopes are connected to onboard electronics and provide an analog output which is processed to provide guidance information to the operator or a computerized control system of the vehicle, for example, a pilot or an onboard computer. With the advent of fiber optic gyroscopes and ring laser gyroscopes, these types of devices have increasingly replaced spinning mass gyroscope systems because of their accuracy and reduced size and weight. Thus, modern day aircraft are constructed with such fiber optic gyroscopes and ring laser gyroscopes, and with appropriate electronics configured for operation with the fiber optic gyroscopes or ring laser gyroscopes. When employed, the output of these newer types of devices is digital in nature and the electronics employed is adapted for processing the digital output for use in vehicle navigation. Although such modern vehicles are increasingly constructed with the fiber optic gyroscope systems or ring laser gyroscope as a component thereof, it also has become desirable to replace the spinning mass gyroscope systems of older vehicles with the more modern and lighter fiber optic gyroscopes or ring laser gyroscopes. (see e.g. Proceedings of the IEEE 1986 National Aerospace and Electronics Conference NAECON 1986, Dayton, Ohio (USA), 19-23 May 1986, pp 1115-1119, R. Cox et al..) A problem with such replacement however, is that the electronics on the older vehicles are configured for operating with the spinning mass system and it has been thought that to implement such fiber optic gyroscopes or ring laser gyroscopes in older vehicles, the entire electronics must be converted to the type presently in use with the newer types of devices. This can be costly and cumbersome. In accordance with the invention, retro-fitting of the entire electronics of older systems is avoided while permitting replacement of the older spinning mass-type gyroscopes with the more modern fiber optic gyroscope or ring laser gyroscope systems. In accordance with the invention as characterized in claim 1 there is provided an interface circuit for use in connecting a rotation sensor and its associated electronics having a digital pulse output to a rotation measuring system for use with a spinning mass rotation sensor. For purposes of this disclosure, the term "associated electronics" means conventional electronics used to provide loop closure for the rotation sensor and condition the sensor outputs to provide digital pulsed outputs where the pulses represent incremental clockwise and counterclockwise rotation. The interface circuit includes a first switch for receiving clockwise pulses from a rotation sensor and its associated electronics, such as a fiber optic gyroscope, which pulses are indicative of changing angular position in one direction. The switch serves to apply a predetermined voltage to a summing integrator for an amount of time equal to the width of the pulses received from the rotation sensor and its associated electronics indicative of changing angular position in a specific direction. A second switch serves the same purpose as the first switch but is for receiving counterclockwise pulses from the rotation sensor and its associated electronics. This switch also applies a predetermined voltage to the summing integrator for an amount of time equal to the width of the counterclockwise pulses received from the rotation sensor and its associated electronics. A convertor receives a command signal representative of change in angular position commanded to a platform on which the position sensor and its associated electronics is mounted. and serves to convert the signal to a voltage proportional to the voltage applied by the first and second switches. The convertor also supplies the converted signal to the summing integrator. The summing integrator then receives the three voltages from the switches and converts and sums the voltages to generate an error output in volts per degrees per second when the command signal is not equal to the converted output from the rotation sensor and its associated electronics. More specifically, the error signal indicates how much the vehicle did not move versus the desired rate for a given amount of time. Further details and improvements of the invention are described in the dependent claims. In a more specific aspect. resistors are connected to the output of the two switches for generating predetermined output charges which are applied to a capacitor connected across the input and output of the summing integrator. The circuit may include a ring laser gyroscope and its associated electronics in place of the fiber optic gyroscope and its associated electronics. Since many ring laser gyroscopes have a means of providing a sinusoidal modulation about the input axis, popularly referred to as dither, to improve the sensitivity and accuracy of the gyroscope at low input rates, this dither motion appears in the clockwise and counterclockwise pulse outputs of many ring laser gyroscopes and must be removed. If this dither modulation is present in the ring laser gyroscope to be used in this invention, this invention also provides a simple means of removing this dither modulation, which consists of a resistor from a point in the normal dither control loop electronics where a buffered signal representing the dither rate motion exits to the summing point of the integrator. The polarity of this dither rate motion signal must be such that the integrator will ramp in a direction opposite that which the result of dither motion in the clockwise/counterclockwise pulses will cause the integrator to ramp, so as to cancel out the dither component of the signal in the integrator output. Thus, in accordance with the invention there is a provided a simple interface circuit which enables substitution of different types of digital rotation sensors in place of analog rotation sensors in existing systems without requiring expensive and/or extensive retro-fitting of the electronics on board existing aircraft and other guided vehicles. BRIEF DESCRIPTION OF THE DRAWINGS Having generally described the invention, the same will become better understood from the following detailed description taken in conjunction with the attached drawings wherein: Fig. 1 is a schematic block diagram of the interface circuit in accordance with the invention shown connected to a fiber optic gyroscope; Fig. 2 is a detailed circuit diagram of the interface circuit in accordance with the invention showing the specific components thereof; and Fig. 3 is a block diagram showing a specific circuit adaptation for the interface circuit of the invention for use with a ring laser gyroscope. DETAILED DESCRIPTION OF THE INVENTION Fig. 1 generally illustrates in schematic form an interface circuit 11 in accordance with the invention. More particularly, the interface circuit 11 is shown connected to a fiber optic gyroscope 13 and its associated electronics 13' which generates through leads 15 and 17 clockwise and/or counterclockwise pulses indicative of rotation in one direction or another to indicate a change in angular position. The pulses are passed through lines 15 and 17 to a pulse rate adjustment unit 21 which includes two switches 23 and 25 which close upon receipt of a clockwise or counterclockwise pulse respectively, to apply a voltage for a Δt time which is a function of the width of the pulses received. The voltages are applied through matching resistors R to an integrator 27. Prior to passing the voltages to the integrator 27, they are summed at summer 29 with a command signal which has been previously passed by line 31 through amplifier 33. The command signal is indicative of volts per degrees per second. As also shown, the pulse rate adjustment unit 21 dumps a charge equal to for each clockwise or counterclockwise pulse into the capacitor 35 which is connected across the input and output of the integrator 27. For example, a clockwise pulse would add the above charge to capacitor 35, while a counterclockwise pulse would subtract this charge from capacitor 35. The output of amplifier 33 is a current proportional to the degrees per second commanded and also dumps a charge into capacitor 35 through resistor RCOM. The integrator 27 sums these currents from summer 29 and generates an error in degrees when the command signal in volts per degree per second is not equal to the output pulse weight of the actual angular rate input from switches 23 and 25. Alternatively if the command signal is equal to the output of the pulse rate adjustment unit 21, the result is a zero error signal. The invention is shown in greater detail as circuit 41 of Fig. 2 which is a more detailed implementation of the circuit of Fig. 1 showing specific components employed therein. In Fig. 2 the clockwise and counterclockwise pulses are transmitted through lines 15 and 17 to analog switches 23 and 25 which are part of the pulse rate adjustment unit 21 of Fig. 1, are shown in greater detail in Fig. 2 and are respectively connected to positive and negative references 67 and 69. Upon a pulse being received, the respective switch 23 or 25 is closed for a time Δt corresponding to the width of each pulse. The switches 23 and 25 provide an output which is a known voltage, positive for clockwise and negative for counterclockwise, through a matched set of resistors R through line 43 to a summing integrator consisting of a capacitor 45 and an operational amplifier 47, with the capacitor connected across an input 49 and output 51 of amplifier 47. The operational amplifier 47 is connected to ground through line 53 and otherwise connected within the circuit 41 in a conventional manner. The voltage out of each switch 23 and 25 is divided by a resistance provided by matched resistors R at the output thereof to provide a charge to capacitor 45, as noted previously, equal to This average of the charge provided to the operational amplifier 47 by the pulses from the fiber optic gyroscope 13 is a current which is proportional to the degrees per second that the sensor is experiencing as a result of movement. On the bottom half of the circuit 41, there is provided a command signal in volts per degrees per second through line 31 through resistor RIN and lead 55 to an operational amplifier 57 having another resistor RIN2 connected across the input line 55 and an output line 59. The operational amplifier 57 is also connected to ground through line 61 in a conventional manner and passes through resistor RCOM a negative current equal to which is proportional to the degrees per second commanded. The operational amplifier 47 then sums all the currents to create an error output signal in volts per degree when the command signal in volts per degrees per second is not equal to the output pulse weight of the actual angular rate. The resistances at the output of the switches 23 and 25 and at the output of operational amplifier 57 at RCOM are selected in a manner well known to those of ordinary skill in the art to provide proper scaling of the command to the pulse weight, and to allow for closed loop control. Thus, in accordance with the invention, it is possible to employ an inertial sensor with a pulse output such as a fiber optic gyroscope to emulate a spinning mass gyroscope within presently existing spinning mass gyroscope guidance systems. In another variation of this invention, a ring laser gyroscope 71 and its associated electronics 73 may be substituted in place of the fiber optic gyroscope and its associated electronics. If the ring laser gyroscope does not have any dither modulation components in its clockwise and counterclockwise pulse outputs, then the block diagram for the ring laser gyroscope variation of this invention is identical to Figure 1, except that the fiber optic gyroscope 13 and its associated electronics 13' would be replaced with the ring laser gyroscope 71 and its associated electronics 73. If dither modulation is present in the ring laser gyroscope to be used in this invention, then the block diagram in Figure 3 better represents the invention. The difference between Figure 3 and Figure 1 is that Figure 3 also includes a simple means of removing this dither modulation, which consists of a resistor Rd from a point in the normal dither control loop electronics 75 where a buffered signal representing the dither rate motion exists from dither motor/pickoff 77 through pickoff lead 79 through a preamplifier 81 and lead 83 and through resistor Rd to the summer 29 of the integrator 27. The polarity of this dither rate motion signal must be such that the integrator 27 will ramp in a direction opposite that which the result of dither motion in the clockwise/counterclockwise pulses will cause the integrator 27 to ramp, so as to cancel out the dither component of the signal in the integrator output. The value of this resistor Rd is chosen such that, if dither modulation is the only motion present about the input axis of the gyroscope, then, for a given amount of dither motion, the change in the output of the integrator due to the signal through the resistor Rd is equal and opposite to the change in the integrator output due to clockwise and counterclockwise pulse outputs.

Claims: An interface circuit for use in connecting a rotation sensor (13; 71) and its associated electronics (13', 73) with a digital pulse output (15, 17) to a rotation measuring system for use with a spinning mass rotation sensor characterized by a) first switch means (23) for receiving clockwise pulses from a rotation sensor (13) and its associated electronics (13') indicative of change in angular position and for generating and applying a predetermined voltage to summing integrating means (29, 27; 47, 45) for an amount of time (Δt) equal to the width of pulses received from said rotation sensor and its associated electronics; b) second switch means (25) for receiving counterclockwise pulses from said rotation sensor and its associated electronics indicative of change in angular position and for generating and applying a predetermined voltage to summing integrating means (29) for an amount of time (Δt) equal to the width of pulses received from said rotation sensor and its associated electronics; c) converting means (33; 57) for receiving a command signal representative of change in angular rate commanded to a platform on which said rotation sensor (13) and its associated electronics (13') is mounted, for converting said signal to a voltage proportional to the voltages applied by said first (23) and second (25) switch means and for applying said converted signal to summing integrating means (29, 27; 47, 45); and d) summing integrating means (29, 27; 47, 45) for receiving said voltages from said first and second switch means (23, 25) and said converting means (33) for summing the voltages applied thereto for generating an error output in volts per degrees per second when the command signal is not equal to the converted output from said rotation sensor and its associated electronics. The interface circuit of claim 1, characterized by : a) first resistor means (R) connected to the output of said first switch means (23) for generating a predetermined first output charge to be applied across said summing integrating means (29, 27, 47, 45); b) second resistor means (R) connected to the output of said second switch means (25) for generating a predetermined second output charge to be applied across said summing integrating means; and c) third resistor means (RCOM) connected to the output of said converting means (33; 57) for generating a predetermined third output charge to be applied across said summing integrating means. The interface circuit of claim 1 or 2, characterized by a capacitor means (35, 45) connected across the input and output of said summing integrating means (27; 47) for having said first, second and third output charges applied thereto. The interface circuit of claim 1, 2 or 3, characterized in that said summing integrating means is an operational amplifier (27; 47). The interface circuit of claim 1, 2 or 3, characterized in that said converting means is an operational amplifier (27; 47) connected to operate as an inverting buffer for said command signal. The interface circuit of one of the preceding claims, characterized by having converting means for directly connecting said first and second switch means (23,25) to a fiber optic gyroscope (13). The interface circuit of one of the preceding claims, characterized by converting means for directly connecting said first and second switch means (23, 25) to the clockwise and counterclockwise pulse outputs (15, 17) of a ring laser gyroscope (71) and its associated electronics (73). The interface circuit of claim 7, characterized in that said ring laser gyroscope (71) has dither control loop electronics (75), and further comprising a resistor (Rd) connected to said dither control electronics (75) and to said summing integrating means (29, 27, 35) at a point where a signal representing the dither rate motion of said ring laser gyroscope is present with a polarity such that, when it is applied to the input of said summing integrating means, dither modulation received by said summing integrating means from said connection through said first and second switch means (23,25) to said ring laser gyroscope (71, 73) which is normally present in the output of the said summing integrating means is canceled.

Inventors: DESMARAIS RICHARD R, KARPINSKI ANDREW J JR, DESMARAIS, RICHARD R., KARPINSKI, ANDREW J., JR.
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1994
Main classification: G01C19
IPC codes: G01C21, G01C19